Automated bricklaying machinery was proposed in U.S. Pat. No. 4,060,955, granted on Dec. 6, 1977 to Lachnit. The machinery includes a main carriage that rolls on horizontal tracks. The main carriage supports a bricklaying machine and a pallet bearing a large supply of stacked bricks. The bricklaying machine has a frame that displaces vertically on uprights fixed to the main carriage. The frame supports a magazine that contains a single vertical stack of bricks, and also supports a pair of horizontal rails. The horizontal rails in turn support a secondary carriage to which a brick-gripping mechanism and a mortar injector are mounted. In operation, the secondary carriage is first positioned beside the brick magazine. A hydraulically-operated lever mechanism transfers a single brick from the magazine to the brick gripper. The secondary carriage then travels along the horizontal rails until the mortar injector and the brick gripper are appropriately positioned to apply mortar and place the gripped brick beside the current flight. When the magazine is empty, another hydraulically-operated mechanism grips a row of bricks on the pallet and reorients the row as a vertical stack in the magazine.
There are several shortcomings to the proposed machinery. Dispensing mortar under pressure is not reliable in an automated process, as mortar has a tendency to clog pumps and conduits. Also, vertical joints between bricks cannot be readily filled. The machinery also requires excessive brick handling. Bricks must be stacked on a pallet, then re-stacked in a magazine, and finally transferred to a brick gripper. The apparatus is also very dependent on precise leveling and positioning of the rails supporting the main carriage.
A variety of robotic mechanisms for placing concrete blocks are canvassed in an article by Slocum and Shena entitled "Blockbot: A Robot To Automate Construction Of Cement Block Walls", published in Robotics & Automation Systems, v. 4, No. 2, June, 1988. One robotic mechanism described in the article includes an arm assembly somewhat similar to that proposed in the present specification. It has an upper arm and a forearm together with appropriate shoulder, elbow and wrist joints that pivot about parallel horizontal axes. The wrist joint supports a block-gripping mechanism. Such an arm assembly is dismissed as having insufficient stiffness and load-bearing capacity and as requiring excessively complex control.
The article suggests use of a robotic arm with a single horizontal arm member. The arm member swings about a vertical axis at a shoulder joint, and the shoulder joint can itself be raised and lowered on a vertical track. A wrist joint between the arm and a block gripping mechanism allows only pivoting of the gripping mechanism about a vertical axis. The robotic arm is mounted on a horizontal track fixed to a wheeled carriage. The carriage has a platform on which a store of individual blocks is rested. In operation, the carriage is moved to a desired location and kept stationary. The arm assembly displaces horizontally along the track in increments correspond to successive block positions in the masonry being constructed. The arm swings horizontally over the platform and lowers to receive a block. The arm then raises, swings horizontally to locate the block over the masonry, and lowers to seat the block on the masonry.
The article proposes that blocks be stacked dry. It suggests that a bonding layer be formed over the exterior of the resulting masonry. There are several shortcomings, however. Precision blocks may be required as there is no bonding composition between blocks to accommodate variations in size. Also, bricks are preferred to blocks largely for esthetic reasons, and placing a bonding layer over brick masonry defeats the basic purpose for using bricks. A number of issues are not adequately addressed, such as how to align the carriage when moved to successive positions along the masonry, and how to supply blocks to the block laying machinery.
The present specification addresses several problems relating to automation of bricklaying. These relate to mortar application, appropriate construction of a robotic arm assembly, how to conveniently supply mortar and bricks to automated bricklaying equipment, and reducing sensitivity of such equipment to variations in the orientation of a guideway or track.